Characterizing droplet combustion of pure and multi-component liquid fuels in a microgravity environment

The importance of understanding the effects of fuel composition, length scales, and other parameters on the combustion of liquid fuels has motivated the examination of simple flames which have easily characterized flow fields and hence, the potential of being modeled accurately. One such flame for liquid fuel combustion is the spherically symmetric droplet flame which can be achieved in an environment with sufficiently low gravity (i.e., low buoyancy). To examine fundamental characteristics of spherically symmetric droplet combustion, a drop tower facility has been employed to provide a microgravity environment to study droplet combustion. This paper gives a brief review of results obtained over the past three years under NASA sponsorship (grant NAG3-987)

Increased perceptual distraction and task demand enhances gaze and non-biological cuing effects.

This study aims to improve understanding of how distracting information and target task demands influence the strength of gaze and non-biological (arrow and moving line) cuing effects. Using known non-predictive central cues, we manipulated the degree of distraction from additional information presented on the other side of the target, and target task difficulty. In Experiment 1, we used the traditional unilateral cuing task, where participants state the location of an asterisk and the non-target location is empty (no distraction). Experiment 2 comprised a harder localisation task (which side contains an embedded oddball item) and presented distracting target-related information on the other side. In Experiment 3, we used a discrimination task (upright or inverted embedded T) with distracter information that was unrelated or related to the target (low vs. high distraction, respectively). We found that the magnitude of cuing scaled with the degree of combined distraction and task demands, increasing up to six-fold from Experiments 1 and 2 to the high-distraction condition in Experiment 3. Thus, depleting attentional resources in this manner appears to weaken the ability to ignore uninformative directional cues. Findings are discussed within the framework of a resource-limited account of cue inhibition

Barriers block the effect of joint attention on working memory:Perspective taking matters

Joint focus of attention between two individuals can influence the way that observers attend, encode, and value items. Using a nonpredictive gaze cuing task we previously found that working memory (WM) was better for jointly attended (validly cued) versus invalidly cued colored squares. Here we examine whether this influence of gaze on WM is driven by observers sharing the perspective of the face cue (mental state account), or simply by increased attention to the cued location (social attention account). To manipulate perspective taking, a closed barrier obstructed the cue face’s view of the memoranda, while an open barrier allowed the cue face to “see” the colors. A central cue face flanked by two identical barriers looked left or right, followed 500 ms later by colored squares for encoding which appeared equally often in the validly and invalidly cued locations. After a blank 1000 ms maintenance interval, participants stated whether a probe color was present or not in the preceding display. When the barrier was open, WM was significantly impaired for invalidly versus validly cued items. When the barrier was closed, the effect of gaze cues on WM was abolished. In contrast, further experiments showed a significant cuing effect on the speed of simple target localization and color discrimination regardless of barrier type. These findings support the mental state account of joint attention in WM, whereby the attentional focus of another alters WM via higher level engagement with the second person perspective. A goal-specific model of perspective taking is proposed

Joint attention enhances visual working memory.

Joint attention—the mutual focus of 2 individuals on an item—speeds detection and discrimination of target information. However, what happens to that information beyond the initial perceptual episode? To fully comprehend and engage with our immediate environment also requires working memory (WM), which integrates information from second to second to create a coherent and fluid picture of our world. Yet, no research exists at present that examines how joint attention directly impacts WM. To investigate this, we created a unique paradigm that combines gaze cues with a traditional visual WM task. A central, direct gaze ‘cue’ face looked left or right, followed 500 ms later by 4, 6, or 8 colored squares presented on one side of the face for encoding. Crucially, the cue face either looked at the squares (valid cue) or looked away from them (invalid cue). A no shift (direct gaze) condition served as a baseline. After a blank 1,000 ms maintenance interval, participants stated whether a single test square color was present or not in the preceding display. WM accuracy was significantly greater for colors encoded in the valid versus invalid and direct conditions. Further experiments showed that an arrow cue and a low-level motion cue—both shown to reliably orient attention—did not reliably modulate WM, indicating that social cues are more powerful. This study provides the first direct evidence that sharing the focus of another individual establishes a point of reference from which information is advantageously encoded into WM

Cosmic D-Strings and Vortons in Supergravity

Recent developments in string inspired models of inflation suggest that D-strings are formed at the end of inflation. Within the supergravity model of D-strings there are 2(n-1) chiral fermion zero modes for a D-string of winding n. Using the bounds on the relic vorton density, we show that D-strings with winding number n>1 are more strongly constrained than cosmic strings arising in cosmological phase transitions. The D-string tension of such vortons, if they survive until the present, has to satisfy 8\pi G_N \mu \lesssim p 10^{-26} where p is the intercommutation probability. Similarly, D-strings coupled with spectator fermions carry currents and also need to respect the above bound. D-strings with n=1 do not carry currents and evade the bound. We discuss the coupling of D-strings to supersymmetry breaking. When a single U(1) gauge group is present, we show that there is an incompatibility between spontaneous supersymmetry breaking and cosmic D-strings. We propose an alternative mechanism for supersymmetry breaking, which includes an additional U(1), and might alleviate the problem. We conjecture what effect this would have on the fermion zero modes.Comment: 11 page

Ariel - Volume 4 Number 6

Editors David A. Jacoby Eugenia Miller Tom Williams Associate Editors Paul Bialas Terry Burt Michael Leo Gail Tenikat Editor Emeritus and Business Manager Richard J. Bonnano Movie Editor Robert Breckenridge Staff Richard Blutstein Mary F. Buechler J.D. Kanofsky Rocket Weber David Maye

Prospectus, July 23, 1991

https://spark.parkland.edu/prospectus_1991/1010/thumbnail.jp

A short-duration dark adaptation protocol for assessment of age-related maculopathy

Dark adaptometry may be a useful diagnostic test and clinical trial endpoint for age-related maculopathy (ARM) because impaired night vision is a hallmark of early ARM. A novel dark adaptometer, the AdaptDx, was evaluated for the detection of ARM. The AdaptDx incorporates a 20-minute protocol optimized for the detection of ARM. ARM patients (N = 17) exhibited substantial dark adaptation impairment compared with normal adults (N = 17). The diagnostic sensitivity was 88% and the specificity was 100%. The diagnostic test characteristics of the AdaptDx are similar to previously reported studies using 60- to 120-minute protocols

Casimir-Polder interaction between an atom and a small magnetodielectric sphere

On the basis of macroscopic quantum electrodynamics and point-scattering techniques, we derive a closed expression for the Casimir-Polder force between a ground-state atom and a small magnetodielectric sphere in an arbitrary environment. In order to allow for the presence of both bodies and media, local-field corrections are taken into account. Our results are compared with the known van der Waals force between two ground-state atoms. To continuously interpolate between the two extreme cases of a single atom and a macroscopic sphere, we also derive the force between an atom and a sphere of variable radius that is embedded in an Onsager local-field cavity. Numerical examples illustrate the theory.Comment: 9 pages, 4 figures, minor addition